Injection molding nozzle having grounded heating element brazed into pointed tip

ABSTRACT

This invention relates to an improved injection molding nozzle having an integral electrical heating element. The nozzle has an elongated nose portion extending to a forward end from a cylindrical central portion. The heating element is brazed in a spiral channel around a central melt bore in the central portion of the nozzle, and extends into the nose portion to a forward end which is grounded by brazing it in nickel adjacent a high speed steel insert portion at the forward end of the nozzle. This forms a pointed tip at the forward end of the nozzle which is corrosion and wear resistant and can be heated to a predetermined temperature. In alternative embodiments, the forward end of the heating element can be brazed in nickel adjacent the forward end without the high speed steel insert portion and/or the nose portion can be inclined with the forward end of the heating element being grounded adjacent an end gate rather than a separate gate. The mass of the central portion and the elongated tapered shape of the nose portion which permits relatively rapid temperature changes of the melt in the gate area enable the nozzle having a single heating element to be used for temperature assisted gating.

BACKGROUND OF THE INVENTION

This invention relates to injection molding and more particularly to animproved injection molding nozzle having an integral electrical heatingelement wherein the forward end of the heating element is brazed intothe nose portion to ground it and heat the forward end of the nozzle.

Nozzles with integral heating elements are well known in the art. Forexample, the applicant's recent Canadian patent application Ser. No.542,185 entitled "Coated Injection Molding Nozzle and Method" filed July15, 1987 discloses a nozzle in which the forward end of the heatingelement extends into the nose portion. It is also known to provideinjection molding probes having two heating elements, one of which iswelded at the pointed tip to ground it. Examples of this are shown inU.S. Pat. No. 4,516,927 to Yoshida which issued May 14, 1985 and U.K.patient application No. 2,164,893A to Tsutsumi filed Aug. 25, 1985.While these previous probes are used to temperature gate the flow ofmelt, the fact that the melt flows around each probe between it and thesurrounding cooled cavity plate necessitates the use of two heatingelements so the main one can be energized continuously to avoid anunacceptable temperature drop in the melt. In the present invention, themelt flows through the heated nozzle and a single heating element can beused to heat both the central portion and the nose portion of thenozzle.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to at leastpartially overcome the disadvantages of the prior art by providing anozzle with a single integral heating element, the forward end of whichextends into the nose portion of the nozzle and is brazed in anelectrically conductive material to ground it adjacent the forward endof the nozzle.

To this end, in one of its aspects, the invention provides an elongatedintegral injection molding nozzle having a forward end and a rear endwith a central portion having a generally cylindrical outer surfaceextending between a steel collar portion adjacent the rear end and anose portion adjacent the forward end, the nose portion having a taperedouter surface leading to the forward end, the nozzle having a melt borewith a first and second portion, the first portion extending centrallyfrom the rear end through the central portion and joining the secondportion which extends diagonally to the tapered surface of the noseportion, the nozzle having an electrically insulated heating elementintegrally brazed in a spiral channel in the cylindrical outer surfaceof the central portion with a portion extending diagonally into the noseportion to a forward end and a rear end extending out through a radialopening in the collar portion to a cold terminal, the heating elementhaving a resistance wire extending centrally through an electricalinsulating material in an outer casing, the outer surface of the centralportion and the heating element brazed in the spiral channel thereinbeing covered with a protective coating, the improvement wherein thecentral resistance wire at the forward end of the heating element isexposed and integrally brazed in an electrically conductive brazingmaterial to ground the heating element adjacent the forward end of thenozzle, whereby the forward end of the nozzle can be heated to apredetermined temperature.

Further objects and advantages of the invention will appear from thefollowing description, taken together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a portion of an injection molding system,showing a nozzle according to a preferred embodiment of the invention;

FIG. 2 is an enlarged view showing the pointed tip of the nose portionof the nozzle seen in FIG. 1;

FIG. 3 is a sectional view of the nozzle seen in FIG. 1 showing thethermocouple hole; and

FIG. 4 is a sectional view of a portion of an edge gated injectionmolding system, showing a nozzle according to a second embodiment of theinvention.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference is first made to FIG. 1 which shows a portion of amulti-cavity injection molding system wherein a number of heated nozzles10 extend from a common elongated heated manifold 12. Each heated nozzle10 is seated in a well 14 in a cavity plate 16. The nozzle 10 has asteel central portion 18 with a generally cylindrical outer surface 20extending between a steel collar portion 22 adjacent the rear end 24 anda steel elongated nose portion 26 adjacent the forward end 28. The noseportion 26 has a tapered outer surface 30 which leads to a pointed tip32 at the forward end 28 which is in alignment with a gate 34 in thecavity plate 16 leading to a cavity 36.

The nozzle 10 is seated in this position in the well 14 by acircumferential insulation flange or bushing 38 which extends from thecollar portion 22 and sits on a circumferential shoulder 40. The nozzleis accurately located with the pointed tip 32 in alignment with the gate34 by a circumferential sealing and locating flange 42 which extendsbetween the central portion 18 and the nose portion 26 to abut againstthe inner surface 44 of the well 14. As can be seen, other than theinsulation flange 38 and the sealing and locating flange 42, the heatednozzle 10 is separated from the surrounding cooled cavity plate 16 by aninsulative air space 46.

Each nozzle 10 is fastened by bolts 48 to the manifold 12 which issecured between the cavity plate 16 and a back plate 50 by a locatingring 52 and a titanium pressure pad 54. The back plate 50 is held inplace by bolts 56 which extend into the cavity plate 16. The back plate50 and the cavity plate 16 are cooled by pumping cooling water throughcooling conduits 58. The manifold 12 is heated by an electric heatingelement 60 which is cast into it as described in the applicant's U.S.Pat. No. 4,688,622 entitled "Injection Molding Manifold Member andMethod of Manufacture" which issued Aug. 25, 1987. The locating ring 52provides another insulative air space 62 between the heated manifold 12and the cooled cavity plate 16.

The manifold 12 has a melt passage 64 which branches from a common inletto a number of outlets 66 on the opposite side. Each outlet is inalignment with an inlet 68 to a melt bore 70 extending through one ofthe nozzles. Each melt bore 70 has a central portion 72 extending fromthe rear end 24 and a diagonal portion 74, which connects to the taperedsurface 30 of the nose portion 26.

The nozzle 10 is heated by an electrically insulated heating element 76which is integrally brazed in a spiral channel 78 in the cylindricalouter surface 20 of the central portion 18. The heating element 76 inthe channel 78 and the outer surface 20 are covered with a protectivenickel coating 80 as described in the applicant's Canadian patentapplication Ser. No. 542,185, mentioned above. The heating element 76also has a portion 82 which extends diagonally into the nose portion 26of the nozzle 10 beneath the circumferential sealing and locating flange42 and then centrally to a forward end 84 adjacent the pointed tip 32.As clearly seen in FIG. 3, the low voltage single wire heating element76 has a nickel-chrome resistance wire 86 extending centrally through arefractory powder electrical insulating material 88 such as magnesiumoxide inside a steel casing 90. At the forward end 84 of the heatingelement 76, the exposed resistance wire 86 projects from the insulatingmaterial 88 and casing 90 to a high speed steel insert portion 92 whichforms the pointed tip 32. The exposed wire 86 and the high speed steelinsert portion 92 are integrally brazed in nickel 94 which grounds theheating element 76 adjacent the pointed tip. This provides a pointed tipwhich is corrosion and wear resistant and which can be heated by theheating element 76 to a predetermined temperature. The heating element76 has a rear end 96 which extends out through a radial opening 98 in aplug 100 received in the collar portion 22. The resistance wire 86 atthe rear end 96 of the heating element 76 connects to a threaded stud102 surrounded by ceramic insulation 104 inside a cylindrical steelsleeve 106 which is attached to the surface 108 of the plug 100. Aceramic washer 110 and a steel washer 112 are received on the projectingstud 102 to form a cold terminal 114 which receives an external powerlead 116 which is held securely in place by nut 118. Thus, electricalcurrent from the lead 116 flows through the heating element 76 to theground at the forward end 84. This heats the nozzle 10 throughout boththe central portion 18 and the nose portion 26 so that the pointed tip32 can be heated to a predetermined temperature.

The nozzle 10 has a thermocouple hole 120 which is drilled diagonallyfrom the outer surface 20 of the central portion 18 to extend beneaththe sealing and locating flange 42 into the nose portion 26. As seen inFIG. 3, this hole 120 removably receives a thermocouple 122 whichextends through the air space 46 to measure the temperature of the noseportion 26 during use.

In use, after the injection molding system has been assembled as shownin FIG. 1 and described above, electrical power is applied through thelead 116 to the heating element 76 in each nozzle 10 and to the heatingelement 60 in the manifold 12 to heat the nozzle 10 and the manifold toa predetermined operating temperature. Pressurized melt from a moldingmachine (not shown) is then introduced into the melt passage 64 in themanifold 12 according to a predetermined cycle in a conventional manner.The pressurized melt flows through the melt bore 70 in each nozzle 10into the space 124 surrounding the tapered surface 30 of the noseportion 26, and then through the gate 34 and fills the cavity 36. Thespace 124 remains filled with melt, a portion of which solidifiesadjacent the cooled cavity plate 16, and the sealing and locating flange42 prevents it escaping into the insulative air space 46. After thecavities are filled, injection pressure is held momentarily to pack andthen released. After a short cooling period, the mold is opened to ejectthe molded products. After, ejection, the mold is closed and injectionpressure is reapplied to refill the cavity. This cycle is continuouslyrepeated with a frequency dependent on the size and shape of thecavities and the type of material being molded.

In an alternative use of the system when a larger diameter gate isdesired and/or an easily stringing crystaline material is being molded,temperature assisted gating can be employed. This involves controllingthe flow of power to the leads 116 to the heating elements 76 in aco-ordinated cycle so that no heat is provided to the nozzles for ashort period of time before and when the mold is opened. The elongatedshape of each tapered nose portion 26 surrounded by the cooled cavityplate 16 results in a temperature drop in the gate area of approximately7°-8° C./second. For most crystaline materials, a temperature drop of20°-25° C. is sufficient to freeze the gate prior to ejection. Rightafter the mold is opened, electrical power is reapplied to heat the meltin the gate area to reopen the gate when injection pressure is reappliedafter injection. While heat is also lost from the central portion 18 ofthe nozzle during the injection period, the air gap insulated steel masssurrounding the melt bore 70 retains sufficient heat so that nosolidification occurs. It will be apparent that the shape and size ofthe nozzle and the periods of the molding cycle are critical to thesuccess of this type of gating using only a single heating element. Thecentral portion 18 of the nozzle 10 must have sufficient mass to retainheat, while the nose portion 26 must be sufficiently tapered andelongated and the forward end 84 of the heating element 76 brazed closeenough to the pointed tip 32 that gate temperature can be lowered andraised relatively quickly.

FIG. 4 illustrates a second embodiment of the nozzle according to theinvention. As many of the elements are identical to those of the firstembodiment described above, elements common to both embodiments aredescribed and illustrated using the same reference numbers. In thisembodiment, the tapered nose portion 26 of the nozzle 10 and thesurrounding surface 44 of the well 14 are inclined to one side, and themelt flows into the cavity 36 through an edge gate 122 rather than acenter gate. However, as can clearly be seen, the forward end 84 of theheating element 76 has the central resistance wire 86 exposed andintegrally brazed in nickel 94 to ground it adjacent the forward end 28and the gate 34. This allows the forward end 28 adjacent the gate to beheated to a predetermined temperature, as described above. The use andoperation of this embodiment in either the conventional gating ortemperature assisted gating modes is essentially the same as thatdescribed above and need not be repeated.

While the description of the nozzle and its use have been given withrespect to preferred embodiments, it is not to be construed in alimiting sense. Variations and modifications will occur to those skilledin the art. For instance, the exposed resistance wire 86 at the forwardend 84 of the heating element can be brazed in nickel to form a pointedtip 32 without the use of a high speed steel insert portion 92. Thisprovides the nozzle 10 with a pointed tip which is corrosion and wearresistant and can be heated to a predetermined temperature as describedabove Reference is made to the appended claims for a definition of theinvention.

What we claim is:
 1. In an elongated integral injection molding nozzlehaving a forward end and a rear end with a central portion having agenerally cylindrical outer surface extending between a steel collarportion adjacent the rear end and a nose portion adjacent the forwardend, the nose portion having a tapered outer surface leading to theforward end, the nozzle having a melt bore with first and secondportions, the first portion extending centrally from the rear endthrough the central portion and joining the second portion which extendsdiagonally to the tapered surface of the nose portion, the nozzle havingan electrically insulated heating element with a rear end and a forwardend, the heating element having one portion extending diagonally intothe nose portion to a forward end of the heating element and anotherportion integrally brazed in a spiral channel in the cylindrical outersurface of the central portion, the rear end of the heating elementextending out through a radial opening in the collar portion to a coldterminal, the heating element having a resistance wire extendingcentrally through an electrical insulating material in an outer casing,the outer surface of the central portion and the heating element brazedin the spiral channel therein being covered with a protective coating,the improvement wherein:the central resistance wire at the forward endof the heating element is exposed and integrally brazed in anelectrically conductive brazing material to ground the heating elementadjacent the forward end of the nozzle, whereby the forward end of thenozzle can be heated to a predetermined temperature.
 2. An injectionmolding nozzle as claimed in claim 1 wherein the brazing material isnickel.
 3. An injection molding nozzle as claimed in claim 2 wherein thenickel brazing material forms a corrosion resistant central pointed tipwhich can be heated to a predetermined temperature.
 4. An injectionmolding nozzle as claimed in claim 2 wherein a high speed steel insertportion is integrally brazed into the nose portion of the nozzle to forma pointed tip, and the exposed resistance wire at the forward end of theheating element is brazed adjacent the high speed steel insert portionto ground the heating element adjacent the pointed tip, whereby thecorrosion resistant pointed tip can be heated to a predeterminedtemperature.
 5. An injection molding nozzle as claimed in claim 4wherein the heating element extends diagonally into the nose portion toa central position and then extends centrally to the forward endadjacent the high speed steel insert portion.
 6. An injection moldingnozzle as claimed in claim 5 wherein the central heating wire projectsfrom the surrounding insulating material and casing at the forward endof the heating element, the projecting heating wire and the adjacenthigh speed steel insert portion being integrally brazed in nickel,thereby grounding the heating element adjacent the pointed tip.
 7. Aninjection molding nozzle as claimed in claim 6 wherein the nozzle has anoutwardly projecting circumferential sealing and locating flange betweenthe central portion and the elongated nose portion.
 8. An injectionmolding nozzle as claimed in claim 7 wherein the nozzle has athermocouple hole extending diagonally beneath the sealing and locatingflange from the surface of the central portion into the elongated noseportion.
 9. An injection molding nozzle as claimed in claim 7 whereinthe collar portion has a circumferential insulation flange which islarger in diameter than the outer surface of the central portion, theflange extending towards the forward end of the nozzle around the outersurface of the central portion to provide an insulative air spacetherebetween.
 10. An injection molding nozzle as claimed in claim 1wherein the central portion of the nozzle has sufficient mass and thetapered nose portion of the nozzle is sufficiently elongated wherebycontrolling electrical power to the heating element with the forward endintegrally brazed adjacent the forward end changes the melt temperaturein the gate area sufficiently rapidly to provide temperature assistedgating.